[gecode-users] assert in propagator cast

[David Rijsman]

Hi Christian,

a little bit delayed but yes you are pretty close with your guessing. I do step 1 and step 2 I do cancel the subscription. Also in the dispose method of the propagator I invoke the dispose method of the council. 

Should I also cancel all the subscriptions of the variables to the advisors in the propagators dispose although I invoke the dispose on the council? I checked the dispose of the council and it also invokes the dispose of the advisors which in my case do cancel the subscriptions.

In the example  in gecode/int/bool/or.hpp you are using the advisor type Advisor in which the cancellation does not take place (in my case it does in the specialized implementation of dispose) so I understand the need to explicitly do it in the dispose of the propagator in your case. But I do not see it in my case....

To give you a little more background, I have a propagator working on tasks, each task has five variables of which one is a boolean. When the boolean becomes false I want to dispose all the advisors on all the five variables associated with this task. When the boolean becomes false, in the advise of the propagator I iterate over all the advisors in the council, cast them to my advisor type, ask the advisor if it belongs to the same task as the boolean, if so it is disposed. I had made an optimization which would stop iterating over the advisors once it disposed  four, this is a mistake as it could have found the advisor of the boolean itself and dispose it, now if I exclude the explicit disposal of the advisor of the boolean variable the problem no longer occurs. I am a little puzzled here how this is related to the assert being raised (a double disposal also raises an assert and I do not see this), I will continue my search but if you have any suggestions that would be great,

Another question for my understanding, who is (responsible for) disposing the advisor when a variable becomes assigned?

thanks,

David Rijsman

>>> 
From: 	"Christian Schulte" <cschulte at kth.se>
To:	"'David Rijsman'" <David.Rijsman at quintiq.com>, <users at gecode.org>
Date: 	10/25/2011 5:48 PM
Subject: 	Re: [gecode-users] assert in propagator cast

Hi David,

Let me do some guessing here:

1) You are using a propagator that uses advisors.
2) The dispose method of your advisors does not unsubscribe the advisor from
the view.
3) The propagator's dispose method disposes the advisors' council without
deleting the advisors subscriptions

Bang! Is that correct?

If yes, there are two ways to fix it:
a) The dispose method of the advisors also unsubscribes, or
b) In the propagator's dispose method you iterate over all advisors and
unsubscribe (The iterator is called Advisors<A> where A is the type of the
advisor). You might want to search for Advisors in gecode/int/bool/or.hpp
for an example.

I hope that helps!

Best
Christian

PS: Sorry for the delay, I was travelling.

--
Christian Schulte, KTH, web.it.kth.se/~cschulte/


-----Original Message-----
From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of David Rijsman
Sent: Monday, October 24, 2011 3:34 PM
To: users at gecode.org 
Subject: [gecode-users] assert in propagator cast

I need some help with an assert being thrown by Gecode, hopefully by an
error I made in a propagator I have created. Is there an obvious candidate
for an error I made in my propagator when this assert is thrown?

The assert is thrown in core.hpp

  forceinline Propagator&
  Advisor::propagator(void) const {
    assert(!disposed());
    return *Propagator::cast(ActorLink::prev());
  }

as a result of an invocation of  Advisor::cast(*a)->propagator().afc() in:


  template<class VIC>
  forceinline double
  VarImp<VIC>::afc(void) const {
    if (degree() == 0)
      return 0.0;
    double d = degree();
    // Count the afc of each propagator
    {
      ActorLink** a = const_cast<VarImp<VIC>*>(this)->actor(0);
      ActorLink** e =
const_cast<VarImp<VIC>*>(this)->actorNonZero(pc_max+1);
      while (a < e) {
        d += Propagator::cast(*a)->afc(); a++;
      }
    }
    // Count the afc of each advisor's propagator
    {
      ActorLink** a =
const_cast<VarImp<VIC>*>(this)->actorNonZero(pc_max+1);
      ActorLink** e = const_cast<VarImp<VIC>*>(this)->base+entries;
      while (a < e) {
        d += Advisor::cast(*a)->propagator().afc(); a++;
      }
    }
    return d;
  }

thanks,

David Rijsman


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